Composite staple fiber and process for producing the same

ABSTRACT

A composite staple fiber, wherein a polymer component A and a polymer component B are alternately arranged in a fiber horizontal cross-section; the fiber periphery is entirely covered with the polymer component A; both the polymer component A and the polymer component A have a substantially flat shape; the lengthwise ends of the polymer component B are located 0.05 to 1.5 μm from the fiber surface; and the weight ratio of the polymer component A to the polymer component B is from 90/10 to 10/90. The composite staple fiber of the present invention is not peeled or split by a carding and a needle punching treatments, but is divided and split in the subsequent water jet entanglement, resulting in flat ultrafine fibers having a sharp-edged structure.

TECHNICAL FIELD

The present invention relates to a composite staple fiber having across-section in which two polymer components are alternately layered.More particularly, the present invention relates to a composite staplefiber having its outer surface covered with one of the polymercomponents that constitute the fiber. More specifically, the presentinvention relates to a composite staple fiber which does not causepeeling or splitting between layered polymer components in the cardingor needle punching treatment of a non-woven fabric production, butcauses cracking in the surrounding polymer in the subsequent dividingand splitting process by a water jet treatment, a buffing treatment,etc., and then causes peeling and splitting between the layered polymercomponents inside the fiber, thereby allowing to obtain a fiberstructure composed of groups of ultrafine fibers of the polymercomponents.

Since a part of the surrounding polymer of the composite staple fiber isbroken in the dividing and splitting process to result in the formationof ultrafine fibers having acute edges, the fiber structure exhibits asuperior wiping capacity when used, for example, as a wiper. Inaddition, since the fiber structure contains ultrafine fibers,artificial leather, spun lace and non-woven fabric for sanitary usehaving soft texture and satisfactory permeability are obtained.Moreover, since composed of densely packed fibers, the fiber structurehas a good water absorption by capillary action, and shows a superiordust-removing performance when used as a filter, a breathing mask, etc.Moreover, sheets made of divided and split composite staple fibers, orsheets obtained by dividing and splitting composite staple fiber sheetshave their own characteristic luster due to the flat, ultrafine fibersformed by splitting.

BACKGROUND ART

Since there are limitations on the fiber fineness due to increasedsusceptibility to breakage during a direct spinning, ultrafine fibershaving a single fiber fineness of 0.1 denier or less have been producedby a conjugate spinning method. Examples of the cross-section of thecomposite fibers for forming ultrafine fibers include: (1) amulti-layered cross-section or a petal-shaped cross-section in whichmany parts of respective two components are separately and mutuallyarranged in layers, and (2) an islands-in-a-sea cross-section in whichone component is finely dispersed in another component. In the formercomposite fibers, ultrafine fibers having sharp edges and ultrafinefibers having modified cross-sections are formed by the peeling of thecomponents, and find various applications depending on their shapes.

Such composite fibers are typically composed of Nylon 6 and polyethyleneterephthalate (PET). The methods for peeling and dividing thesecomponents include (1) a method of separation by shrinking force of theNylon component when treated with a liquid containing a chemical such asbenzyl alcohol, (2) a method of separation by slightly dissolving awaythe PET component with an aqueous alkali solution, (3) a method ofpeeling by repeating wet heat treatment and drying treatment severaltimes, (4) a method of forcible separation by physically scouring orrubbing, and (5) a combination thereof.

It is important in view of productivity to prevent the generation offluff caused by peeling between the composite components during thefiber production process such as the drawing process. Therefore, in acombination of, for example, Nylon 6 and PET, a PET copolymerized with5-sodium sulfoisophthalate is used to improve the adhesion between thecomponents. Alternatively, it has been proposed to prevent the peelingduring the fiber production by spinning the composite fiber at such anincreased spinning speed as to make PET and Nylon to show similarshrinkage behaviors.

However, even in the case of employing the above measures against thefiber splitting, the peeling occurs between the components of thecomposite fiber in the carding process for producing non-woven fabricsor spun yarns from staple fibers, resulting in the problems of thesplitting composite fiber and the generation of neps. In addition, whenthe needle punching is performed to entangle the fibers, the peeling dueto damage occurs to make composite fibers resistant to entanglement,thereby resulting in the problem of failure to increase the peelstrength of the non-woven fabric.

For example, Japanese Patent Application Laid-Open Nos. 4-308224 and5-44127 propose to prevent the peeling and splitting between thecomponents during the carding process of the subdividable compositefiber by covering the fiber surface with one of the components thatcompose the composite fiber.

However, these known techniques are directed to composite fibers of atype in which the surrounding of the composite fibers is dissolved awayafter made into fabrics by the treatment with a solvent, and do notdisclose in any way a composite staple fiber having a surrounding thatis not broken during the carding or needle punching process, but brokenin the subsequent dividing and splitting process such as water jettreatment, etc. to cause the composite staple fibers to be subdividedinto ultrafine fibers.

In addition, in the technique described in Japanese Patent ApplicationLaid-Open No. 4-308224, since ultrafine fibers are formed by dissolvingaway the surrounding made of one of the components that encapsulates theother component, the yield of ultrafine fibers is low, resulting in theproblem of poor production efficiency of ultrafine fibers. In addition,it is difficult to control the surrounding thickness to a desired levelsimply by changing the proportion of both components. The proposedtechnique is adequate for forming ultrafine fibers by entirelydissolving away one of the components with solvent, etc. However, notsuitable for allowing both the components to remain as ultrafine fibersby a mechanical processing method, because the surrounding of theproposed technique is excessively thick thereby preventing the compositefibers from being split adequately.

Japanese Patent Application Laid-Open No. 5-44127 discloses compositelong fibers for constituting composite pre-twisted yarns, and proposes atechnique for inhibiting the fibrillation of composite fibers due tofriction during a pre-twisting process by covering with polyester thesurface of the composites long fibers having a polyamide-polyesterlayered structure. However, it is only described that, after making thecomposite pre-twisted yarn into a woven or knitted fabric, the coveringpolyester is dissolved away by alkali treatment, thereby dividing thecomposite components. Thus, there is no description of a compositestaple fiber which is resistant to the peeling during the carding andthe needle punching treatment of a non-woven fabric production, etc.,but is subdivided into ultrafine fibers by the subsequent mechanicalpeeling and dividing process such as water jet treatment.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a composite staplefiber and a production method thereof, in which there is substantiallyno occurrence of the peeling or splitting between the components thatcompose the composite fiber during the carding process, the needlepunching process, etc., in the production of non-woven fabrics, etc.,but the peeling and splitting between the composite components occuronly in a subsequent physical dividing process such as a water jettreatment. Another object of the present invention is to provide a fiberstructure that contains the above composite staple fiber and shows asuperior wiping performance when used as a wiper. Still another objectis to provide a fiber structure that contains the above composite staplefiber and exhibit a satisfactory texture and satisfactory colordevelopment when used as artificial leather.

Namely, in a first aspect of the present invention, there is provided acomposite staple fiber having a layered composite structure in which apolymer component A and a polymer component B are alternately arrangedin a fiber cross-section, wherein the polymer component B is completelycovered with the polymer component A, the polymer component B and aportion of the polymer component A except for the skin-forming portionhas a substantially flat shape, and in the fiber cross-section, the endsof the polymer component B in the lengthwise direction are located 0.05to 1.5 μm inside the fiber surface, and a weight ratio of the polymercomponent A to the polymer component B is from 90/10 to 10/90.

In a second aspect of the present invention, there is provided a processfor producing a composite staple fiber having a layered compositestructure in which a polymer component A and a polymer component B arealternately arranged in a fiber cross-section, wherein the polymercomponent A and the polymer component B are melt-spun so that asolubility parameter, SP value, and a melt viscosity during themelt-spinning of each component satisfy the following Equation 1:

η_(A)−η_(B)≦−200×(SP_(A)−SP_(B))  1

wherein η_(A) is a melt viscosity (poise) of the polymer component Aduring the melt-spinning, η_(B) is a melt viscosity (poise) of thepolymer component B during the melt-spinning, SP_(A) is a solubilityparameter of the polymer component A, and SP_(B) is a solubilityparameter of polymer component B.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing an example of the compositestaple fiber of the present invention;

FIG. 2a is a cross-sectional view of a flat ultrafine fiber composed ofa polymer component A, formed by dividing a composite staple fiber; and

FIG. 2b is a cross-sectional view of a flat ultrafine fiber composed ofa polymer component B, formed by dividing a composite staple fiber.

BEST MODE FOR CARRYING OUT THE INVENTION

In the composite staple fiber of the present invention, as shown in FIG.1, for example, it is important that the polymer component B becompletely covered with the polymer component A which is present overthe entire periphery in any of the fiber cross-section. In the case thecomponent B is not entirely covered with the component A, in the cardingor needle punching process in the production of a non-woven fabric, forexample, the peeling and splitting in the lengthwise direction of thefiber occur at the interface between the composite components.

In order to form a surrounding near the fiber surface, it is necessarythat the weight ratio of the component A to the component B be withinthe range of 90/10 to 10/90, and preferably 85/15 to 15/85. In the casethe weight ratio of the component B is less than 10%, it becomesdifficult to alternately arrange the component A and the component B ina spinning pack to form the target cross-section. In the case the weightratio of the component B exceeds 90%, it is difficult to obtain thetarget cross-section owing to a small amount of the component A, and italso becomes difficult to cover the entire fiber surface or thesurrounding thickness becomes excessively thin.

In addition, in the present invention, the component B and the componentA except for the portion forming the skin of the composite staple fiber,i.e., the component A sandwiched between two layers of the component B,substantially exhibits a flat shape when viewing the fibercross-section. Moreover, in the fiber cross-section, it is importantthat the lengthwise ends of the component B be located 0.05 to 1.5 μm,preferably 0.1 to 1.0 μm, from the fiber surface owing to the presenceof the surrounding comprised of the component A.

In the case the thickness of the surrounding of the component A formedbetween the fiber surface and the component B is less than 0.05 μm, thesurrounding is broken by abrasion in the carding and needle punchingprocesses, thereby causing the component A and the component B to peeland split each other and having a detrimental effect on the processingsoundness of the non-woven fabric production. On the other hand, if thethickness exceeds 1.5 μm, although the peeling and splitting in thecarding and needle punching processes are adequately prevented, thesplitting of the composite stable fiber into ultrafine fibers becomesdifficult in the subsequent water jet entanglement, etc.

In the present invention, ultrafine fibers composed of the component Aand ultrafine fibers composed of the component B are formed within afiber structure such as non-woven fabric containing the composite staplefibers by subjecting the fiber structure to a splitting processing usinga physical means such as water jet entanglement. In consideration of aperformance as a wiper or a soft feeling and color development as anartificial leather, it is important that both the component A and thecomponent B have a flat cross-section.

For example, when a high-quality artificial leather such as a raisedartificial leather with suede or nubuck finish is produced using thecomposite staple fiber of the present invention, the thinner the singlefibers, the better the hand feeling. Thus, it is preferable to usefibers thinner than 0.1 dtex, namely fibers having a diameter of lessthan about 3 μm. In other words, it is preferable that single fibers ofthe ultrafine flat fibers respectively composed of the component A andthe component B prepared by dividing the composite staple fibers have awidthwise thickness D, indicated in FIGS. 2a and 2 b, of 3 μm or less.If the thickness is greater than 3 μm, the hand feeling becomes poor.

Moreover, in the case of the artificial leather, it is important thatthe color development be satisfactory. In order to achieve this, it ispreferable that the ratio (L/D: flatness) of the length L in thelengthwise direction to the thickness D in the widthwise direction ofthe flat ultrafine fibers shown in FIGS. 2a and 2 b be 2 or more. In thecase the ratio is less than 2, since the color development does notimprove, dyeing must be performed using a large amount of dye to resultin high dyeing costs.

Moreover, although the thinner the thickness D in the widthwisedirection of the flat ultrafine fibers, the better the hand feeling, anda high flatness results in satisfactory color development by dyeing, anexcessively small thickness D and an excessively small fiber finenessresult in a poor color development. Therefore, it is preferable that thesingle fiber fineness of each flat ultrafine fiber be 0.02 dtex or morein order to ensure a good hand feeling and a satisfactory colordevelopment. Although there are no particular restrictions on the upperlimit of the single fiber fineness as far as it is within the range thatenables the exhibition of effects as ultrafine fibers, the upper limitis preferably 0.6 dtex or less.

The dividing and splitting of the composite staple fiber of the presentinvention is mainly performed by a physical means such as a water jettreatment and a buffing treatment. The dividing and splitting occurseasily at the apex of both the roughly arc-shaped, lengthwise ends ofthe component B in the cross-section, namely the position where thesurrounding of the component A is the thinnest. The cross-section of thecomponent A formed as a result of the splitting has a shape of theletter “I” as shown in FIG. 2a, and two tapered projections extend fromeach lengthwise end in the direction roughly perpendicular (60-120°) tothe lengthwise direction. These tapered projections are portions of thesurrounding of the polymer A remaining after the splitting of thecomposite staple fiber.

In the present invention, these tapered projections function as sharpedges, and dirt, etc., can be easily removed by the sharp edgesresulting in the favorable wiping capacity when the fiber structure isused as a wiper. In addition, the wiping capacity can be furtherimproved because the dirt is directly captured in the gaps between theflat ultrafine fibers of the component A and the flat ultrafine fibersof the component B.

Next, the following provides a description of the production method ofthe composite staple fiber of the present invention.

In the present invention, in accordance with known methods, the polymercomponent A and the polymer component B are separately melted inrespective melt extruders, introduced into a spinneret so that thecomponent A and the component B are alternately arranged, and thendischarged from the spinneret. Particularly, in a spinning pack, theends of the component B facing the inner wall surface of the spinningpack become rounded because of its surface tension to form gaps betweenthe component B and the inner wall surface, and as a result thereof, thecomponent A flows into the gaps, thereby obtaining the composite staplefiber of the present invention in which the entire periphery of thefiber cross-section is covered with the component A.

To ensure that the ends of the component B become rounded as describedabove, the solubility parameters (SP values) of the components A and Bin the spinning pack and their melt viscosities at the spinningtemperature must satisfy the specific relationship indicated by Equation1:

η_(A)−η_(B)≦−200×(SP_(A)−SP_(B))  1

wherein η_(A) is a melt viscosity (poise) of the component A during themelt-spinning, η_(B) is a melt viscosity (poise) of the component Bduring the melt-spinning, SP_(A) is a solubility parameter of thecomponent A, and SP_(B) is a solubility parameter of the component B.

The SP values of the component A and the component B in the presentinvention can be calculated according to the method proposed by P. A. J.Small, J. Appl. Chem., 3, 71(1953).

Generally, the ends of a polymer become rounded more easily by itssurface tension with increasing SP value, because the polar groups ofthe polymer are positioned as far away from each other as possible.Accordingly, a higher SP value for the component B than that of thecomponent A results in greater rounding of the ends of the component B.This allows the component A to flow easily into the gaps between thecomponent B and the inner wall surface of the spinneret, and to coverthe entire periphery of the fiber cross-section, making it easier toform a surrounding. However, even if the SP value of the component B ishigher than that of the component A, in the case the melt viscosity ofthe component A at the spinning temperature is excessively higher thanthat of the component B, the effect of melt viscosity overcomes theeffect of the SP value, causing the ends of the component A to becomeeasily rounded and making it difficult to form the surrounding.Therefore, even in the case the SP value of the component B is higherthan that of the component A, it is important that the differencebetween the melt viscosity of the component A and that of the componentB does not exceed 200 times the difference in the SP values.

In addition, since a melt viscosity for the component B higher than thatof the component A during the spinning process results in easierrounding of the ends of the component B, the component A flows easilyinto the gaps between the component B and the inner wall surface of thespinneret, and a surrounding is easily formed that covers the entireperiphery of the fiber cross-section. However, even if the meltviscosity of the component B is higher than that of the component A, inthe case the SP value of the component A during the spinning process isexcessively higher than that of the component B, the effects of the SPvalue overcome the effects of the melt viscosity causing the ends of thecomponent A to be easily rounded and making it difficult to form thesurrounding. Thus, in the case the SP value of the component A is higherthan that of the component B, it is important that the melt viscosity ofthe component B is larger than that of the component A by 200 times thedifference in SP values or more.

As has been described above, the ends of the component B can be roundedand the component A can be made to flow into the gaps between the endsof the component B and the inner wall surface of the spinneret bysetting the SP value balance or the melt viscosity balance of thecomponent A and the component B so as to satisfy the specificconditions. In the present invention, the time taken from the alternatearrangement of the melt components A and B in the spinning pack untilthe arranged components are discharged from the nozzle is preferred tobe longer. Namely, if the time until discharged is long, the component Agoes easily around the component B to facilitate the formation of thesurrounding by the shearing effects due to the contact with the wallsurface of the nozzle during the components A and B dwell in thespinning pack. More specifically, the time is preferably 1.5 to 8 timeslonger, more preferably 2 to 5 times longer than the time generallyrequired in using a spinning pack having a structure for ordinaryspinning. In the case the time is less than 1.5 times longer, it isdifficult to obtain the shearing effects, thereby preventing theformation of the surrounding. In the case the time exceeds 8 timeslonger, the retention time inside the spinning pack becomes excessivelylong and the polymers A and B undergo thermal degradation, resulting inthe occurrence of breakage during the spinning and having a detrimentaleffect on the processing soundness.

After being discharged from the spinneret, the composite staple fiber ofthe present invention can be obtained by following the processes such asdrawing, crimping, drying and cutting in accordance with knownproduction techniques for composite spun fibers.

The components A and B that constitute the composite staple fiber of thepresent invention and the combination thereof can be arbitrarilyselected according to their application and required performance inconsideration of the SP value balance and the melt viscosity balance. Inpreferable combinations of the component A and the component B, thedifference in their SP values is 1 or more. In the case the differencein SP values is less than 1, adhesion at adjoining surfaces increasesbecause of the high compatibility between the polymers. Although this isadvantageous for the processing soundness of the carding process and theneedle punching process, it makes the subsequent dividing and splittingof the composite staple fibers difficult.

In consideration of this point, the components A and B can be selectedfrom the following polymers according to their purpose and application:polyesters such as polyethylene terephthalate-based polymer andpolybutylene terephthalate-based polymer, polyolefins such aspolyethylene and polypropylene, polyamides such as Nylon 6 and Nylon 66,styrene-based polymers, vinyl alcohol-based polymers and ethylene-vinylalcohol-based copolymers. These polymers may be used alone or incombination of two or more as each polymer component.

Polyethylene terephthalate-based polymers and/or polybutyleneterephthalate-based polymers may include one or more other dicarboxylicacid components, oxycarboxylic acid components or diol components as thecopolymerized unit, if necessary. Examples of other dicarboxylic acidsinclude aromatic dicarboxylic acids such as diphenyldicarboxylic acidand naphthalene dicarboxylic acid; ester-forming derivatives of thearomatic dicarboxylic acids; metal sulfonate group-containing aromaticcarboxylic acid derivatives such as dimethyl 5-sodiumsulfoisophthalateand bis(2-hydroxyethyl) 5-sodiumsulfoisophthalate; aliphaticdicarboxylic acids such as oxalic acid, adipic acid, sebacic acid anddodecanedioic acid; and ester-forming derivatives of the aliphaticdicarboxylic acids. Examples of the oxycarboxylic acid componentsinclude p-oxybenzoic acid, p-β-oxyethoxybenzoic acid and theirester-forming derivatives. Examples of the diol components includealiphatic diols such as diethylene glycol, 1,3-propanediol,1,6-hexanediol and neopentyl glycol; 1,4-bis(β-oxyethoxy)benzene;polyethylene glycol; and polybutylene glycol.

In the present invention, the use of a polyester such as polyethyleneterephthalate for the component A and a polyamide such as Nylon 6 forthe component B, each satisfying the above Equation 1 for the SP valuebalance and the melt viscosity balance, is particularly preferable.Since the SP value of polyethylene terephthalate is generally 10.5 andthe SP value of Nylon 6 is generally 13.5, Equation 1 is modified withthese values as η_(A)−η_(B)≦−200×(10.5−13.5)=600. Thus, the degrees ofpolymerization of the respective polymers and spinning conditions shouldbe decided so that the difference in melt viscosities of both polymersduring the spinning operation satisfies this equation. For example, asuitable combination may be selected from polyethylene terephthalatehaving an intrinsic viscosity [η] of 0.5 to 0.8 dl/g (measured in a 1:1mixture of phenol and 1,1,2,2-tetrachloroethane at 30° C.) and aspinning temperature of 275 to 310° C., or Nylon 6 having a relativeviscosity of 1.5 to 4.0 with respect to 96% sulfuric acid (measured at25° C. in a concentration of 1 g/100 ml) and a spinning temperature of235 to 300° C.

The composite form shown by the cross-section of the composite staplefiber of the present invention may be a multilayer form, hollowmultilayer form, a petal form, or a hollow petal form according to theintended application and performance. In the applications as wiper andartificial leather, preferred is the multilayer form in which the layersof the component A and the layers of the component B are alternatelylayered. In addition, the fiber is not limited to a circularcross-section fiber, but may be a modified cross-section fiber.

There are no particular restrictions on the single fiber fineness of thecomposite staple fiber, and it can be arbitrarily selected according tothe particular application over a range of, for example, 0.5 to 30 dtex.In addition, the cut length may also be arbitrarily selected over arange of 1 mm to 20 cm according to the application.

Moreover, the composite staple fiber of the present invention may beincorporated with various additives, if necessary. Examples of additivesinclude catalyst, coloring preventive, heat-resistance improver, flameretardant, fluorescent whitener, delustering agent, colorant, lusteringimprover, antistatic agent, fragrance, deodorizer, bactericide,miticide, and inorganic fine particles. In addition, the additives maybe blended into either or both of the components A and B.

Next, the following provides an explanation of the production method ofthe fiber structure that contains the composite staple fibers of thepresent invention. Basically, the fiber structure may be produced byvarious suitable production methods according to the physical propertiesrequired for each application. For example, a fiber structure can beobtained by carding a raw stock comprising 20 wt % or more of compositestaple fibers and other fibers to prepare a web which is then subjectedto water jet treatment thereby splitting and entangling the compositestaple fibers. Alternatively, a fiber structure can be obtained bycarding a raw stock containing 20 wt % or more of composite staplefibers to prepare a web which is then entangled by a needle punchingtreatment, followed by a splitting treatment by a physical method suchas a buffing treatment.

In addition, a fiber structure can be obtained by making a raw stuffcontaining 20 wt % or more of the composite staple fibers into a fibroussheet form which is then subjected to a splitting and entanglingtreatment by a water jet. Alternatively, a fiber structure can beobtained by entangling the fibrous sheet form by needle punching andthen splitting by a physical method such as buffing. In addition, afiber structure can also be produced by using a raw stuff containing 20wt % or more of the composite staple fibers split in advance by aphysical method.

In the case the composite staple fiber content of the fiber structure isless than 20 wt %, it is difficult to obtain the effects produced by thesharp edge of the flat ultrafine fibers of the component A. Therefore,for example, the wiping performance of a wiper becomes poor, and asheet-form structure fail to give a luster due to the flatcross-sections.

Fibers usable in combination with the composite staple fiber of thepresent invention may be selected from synthetic fibers such aspolyester fiber, Nylon fiber, acrylic fiber, polyvinyl alcohol fiber,polyethylene fiber, polypropylene fiber, and vinyl chloride fiber, ornatural fibers such as pulp, cotton, and hemp. Two or more of thesefibers may be used.

In the present invention, the fiber structure containing the compositestaple fibers may be layered to or entangled with another fiberstructure such as knitted fabric or woven fabric. In addition, thecomposite staple fibers can be split by subjecting a fiber structure toa physical processing after having been entangled.

Although the present invention exhibits its maximum effect in the caseof using water jet entanglement or buffing treatment as the methods fordividing and splitting the composite staple fibers, the dividing andsplitting may be performed by an alkali reduction treatment when thecomponent A is polyester.

The above fiber structure can be used in various applications. Forexample, as-produced fiber structure or a fiber structure impregnatedwith various resins is used as a wiper.

The fiber structure can also be formed into artificial leather by asuitable method in accordance with its intended use. For example, afterpreparing a fiber structure by performing the carding process and needlepunching process, and then splitting the composite staple fibers by achemical method such as alkali reduction using an aqueous sodiumhydroxide, polyurethane resin is impregnated into the resulting fiberstructure, followed by dyeing the surface to obtain artificial leather.

The following provides a detailed explanation of the present inventionthrough its examples. However, the present invention is not limited inany way by the examples.

In the following examples, shown are the combination of the polymersconstituting the composite staple fibers, the thickness of thesurrounding formed thereon, the flatness L/D wherein D is the thicknessand L is the length of the flat ultrafine fibers of its cross-section,the card processing soundness of the composite staple fiber, the needlepunching processing soundness, the ability of splitting by water jetentanglement, the hand feeling of the base fabric for artificialleather, and the color development by dyeing. In addition, the wipingcapability of the web made of the composite staple fibers was evaluated.In addition, the intrinsic viscosity [η] of polyester was measured at30° C. in a 1:1 solvent of phenol and 1,1,2,2-tetrachloroethane, and therelative viscosity of Nylon was measured at 25° C. in a concentration of1 g/100 ml in 96% sulfuric acid.

The surrounding thickness, the flatness L/D, the card processingsoundness, the needle punching processing soundness, the ability ofsplitting by water jet entanglement, the color development by dyeing,and the wiping capability were measured or evaluated by the followingmethods.

Surrounding Thickness of Composite Staple Fiber

A test fiber was immersed in a hot water bath at 100° C. for 10 minuteswith both ends thereof fixed under tension, thereby causing a crack inthe interface between the component A and the component B by theshrinkage difference. Then, the cross section of the resultant fiber wasobserved under a scanning electron microscope to measure the surroundingthickness.

Flatness L/D

The cross section of the same sample fiber after cracking as used in theabove was observed under a scanning electron microscope. In the crosssection, the thickness D and the length L of the flat ultrafine fiber ofeach of the components A and B were measured. The flatness L/D wascalculated from the obtained results.

Single Fiber Fineness of Flat Ultrafine Fibers

The fineness was calculated by multiplying the cross-sectional area(D×L) and the density of each polymer component.

Processing Soundness of Card Treatment

A web was prepared by passing the composite staple fibers through aminiature carding machine so as to achieve a basis weight of 50 g/m²,followed by observation of the presence or absence of neps and thelateral surfaces of the fibers under an optical microscope.

Processing Soundness of Needle Punching Treatment

A web having a basis weight of 180 g/m² was prepared through the cardingand cross-wrapping processes. After needle-punching the web at 1000needles per cm², the inside of the web was observed under a scanningelectron microscope to determine whether the peeling and splitting ofthe composite staple fibers occurred.

Water Jet Entanglement

A web having a basis weight of 50 g/m² was prepared by through thecarding treatment. After performing the water jet treatment at a waterpressure of 30 to 60 kg/cm², the web was observed under a scanningelectron microscope to examine the occurrence of the peeling andsplitting of the composite staple fiber.

Color Development by Dyeing

The surface of the web after the needle punching treatment was buffed tosplit the fibers, followed by dyeing under the following conditions. TheKubelka-Munk K/S value was determined from the reflectance of the web,and on the basis of the results, the color development was ranked by thefollowing four grades.

Dyeing Conditions:

1. Presetting: 170° C.

2. Dispersion dyeing: treated for 40 minutes at 125° C. using adispersion dye (CI Disperse Red 183)

3. Relaxation treatment: treated for 20 minutes at 85° C.

4. Acid dyeing: treated for 40 minutes at 98° C. using an acid dye (CIAcid Red 215)

5. Soaping: treated for 20 minutes at 70° C. using Amyradin D (DaiichiKogyo Seiyaku Co., Ltd.)

6. Final setting: 160° C.

Grades of Color Development:

A: Extremely good (K/S value: greater than 16)

B: Good (K/S value: 14-16)

C: Fair (K/S value: 12-14)

D: Poor (K/S value: less than 12)

Hand Feeling

The hand feeling of the base fabric dyed according to the above methodwas ranked by the following four grades.

A: Extremely soft and smooth

B: Soft and smooth

C: Somewhat hard

D: Hard and rough

Wiping Capability

A circle of 2 cm in diameter was drawn with commercially available Indiaink on a glass plate and allowed to dry. After drying, a 5×5 cm sampleweb was placed on the ink circle, and a 500 g weight was additionallyplaced on the sample web. The web loaded with the weight was moved backand forth over the glass plate at a fixed speed, and the ink circledrawn on the glass was investigated to determined after how many cyclesthe circle disappeared.

EXAMPLE 1

Polyethylene terephthalate (SP value=10.5, [η]=0.58 dl/g) for thepolymer component A and Nylon 6 (SP value 32 13.5, relativeviscosity=2.45) for the polymer component B were alternately arrangedinto eleven layers at a weight ratio (former/latter) of 75/25, and thearranged components were spun by discharging from a nozzle at 285° C.The apparent relative viscosities during spinning were 1000 poise and1200 poise, respectively. After spinning, the as-spun fiber was drawn,crimped mechanically and then cut to a length of 51 μm to obtaincomposite staple fibers having the cross-sectional shape as shown inFIG. 1. The single fiber fineness of the resulting composite staplefibers was 3.3 dtex, and the mean thickness of the surrounding of thecomponent A that covered the fiber periphery was 0.5 μm when measured atfive cross-sections cut at 5 mm intervals. A web composed of ultrafinefibers was prepared using the composite staple fibers through thecarding treatment and the water jet entanglement. Although the fibersplitting was not observed after the carding treatment, the fibers weresplit by the subsequent water jet entanglement.

The observation of the cross-section of the resulting ultrafine fibersunder a scanning electron microscope showed that the ultrafine fiberscomposed of the component A had an I-shaped cross-section, and thetapered projections extended from both the lengthwise ends in adirection nearly perpendicular to the lengthwise direction.

The dirt wiping capability of this web were better than that of a wipermade of round cross-sectional fibers known in the art.

Another web was prepared from the composite staple fibers by sequentialtreatments of carding, cross-wrapping, and needle punching. There wereno problems in the web production, and the processing soundness wasfavorable in any of the processes. In addition, no fiber splitting wasnoticed by the observation of the inside of the web under a scanningelectron microscope.

COMPARATIVE EXAMPLE 1

With the exception of changing the weight ratio of the component A andthe component B to 5/95, fibers were formed in the same manner as inExample 1. However, the surrounding of the component A was not formed onthe periphery of the fibers, thereby making it unsatisfactory. A web wasprepared from the resultant composite staple fibers through the cardingtreatment and the water jet treatment. Another web was prepared throughthe carding, cross-wrapping, and needle punching processes. In both thecases, neps occurred in the carding process, thereby preventing theproduction of webs which were suitable for practical use. In addition,the inside observation of the webs by a scanning electron microscopeshowed that the substantial part of the fibers were split.

COMPARATIVE EXAMPLE 2

With the exception of changing the weight ratio of the component A andthe component B to 95/5, fibers were formed in the same manner as inExample 1. However, the cross-sectional observation of the compositestaple fibers revealed that the components failed to be arranged intoeleven layers, thereby preventing the target fibers from being obtained.

COMPARATIVE EXAMPLE 3

Polyethylene terephthalate (SP value=10.5, [η]=0.55 dl/g) for thepolymer component A and Nylon 6 (SP value=13.5, relative viscosity=3.00)for the polymer component B were alternately arranged into eleven layersat a weight ratio (former/latter) of 90/10, and the arranged componentswere spun by discharging from a nozzle at 285° C. The apparent relativeviscosities during spinning were 500 poise and 2000 poise, respectively.After spinning, the as-spun fiber was drawn, crimped mechanically andthen cut to a length of 51 μm. The single fiber fineness of theresulting composite staple fibers was 3.3 dtex, and the mean thicknessof the surrounding of the component A that covered the fiber peripherywas 2.1 μm when measured at five cross-sections cut at 5 mm intervals.

A web was prepared using the composite staple fibers through the cardingtreatment and the water jet entanglement. The fiber splitting was notobserved after the carding treatment. Although entangled in thesubsequent water jet treatment, the fiber splitting did not occurbecause of the thick surrounding of the component A, thereby failing toobtain a target web composed of ultrafine fibers. In addition, therewere no difference in the wiping capability between the web preparedabove and the web made of a round cross-sectional fibers known in theart.

EXAMPLES 2-6 AND COMPARATIVE EXAMPLES 4-6

As shown in Table 1, with the exception of changing the weight ratios ofthe components (A) and (B), the combination of SP values, and thecombination of melt viscosities, respective multi-layered compositestaple fibers of 11 layers were obtained in the same manner as inExample 1. Respective webs were then formed in the same manner as inExample 1 using the resulting composite staple fibers. The thickness ofthe surrounding of the component A of each composite staple fiber andthe results of the carding, needle punching, and water jet entanglingtreatments of each web are shown in Table 1.

The cross-sectional observation by a scanning electron microscope on thefibers after the fiber splitting showed that the ultrafine fibers of thecomponent A of the present invention had unique cross-sectional shapeshaving projections similar to Example 1.

TABLE 1 Examples 1 2 3 4 5 6 Component A PET PET PET PET PET NY6 (wt %)(75) (67) (90) (20) (67) (67) Component B NY6 NY6 NY6 NY6 NY6 PET (wt %)(25) (33) (10) (80) (33) (33) Fineness (dtex) 3.3 3.3 3.3 3.3 3.3 3.3 SPValue Component A 10.5 10.5 10.5 10.5 10.5 13.5 Component B 13.5 13.513.5 13.5 13.5 10.5 Melt Viscosity (P) Component A 1000 1000 1000 10001000 1000 Component B 1200 1200 1200 1200 800 2000 Surrounding Thickness0.5 0.4 1.5 0.1 0.3 0.3 (μm) Fiber Thickness (D) (μm) Component A 2.42.2 2.4 0.5 2.1 2.7 Component B 1.2 1.6 0.4 2.9 1.5 1.3 Flatness (L/D)Component A 5.0 5.5 6.3 32 6.2 4.4 Component B 10 7.5 38 5.5 8.7 9.2Fineness (dtex) Component A 0.41 0.37 0.50 0.11 0.37 0.37 Component B0.17 0.22 0.07 0.53 0.22 0.22 Processing Soundness Carding no* no* no*no* no* no* Needle Punching no* no* no* no* no* no* Water JetEntanglement yes* yes* yes* yes* yes* yes* Comparative Examples 1 2 3 45 6 Component PET PET PET PET NY6 NY6 (wt %) (5) (95) (90) (67) (67)(67) Component B NY6 NY6 NY6 NY6 PET PET (wt %) (95) (5) (10) (33) (33)(33) Fineness (dtex) 3.3 3.3 3.3 3.3 3.3 3.3 SP Value Component A 10.510.5 10.5 10.5 13.5 13.5 Component B 13.5 13.5 13.5 13.5 10.5 10.5 MeltViscosity (P) Component A 1000 1000 500 2000 1200 2000 Component B 12001200 2000 1200 800 1000 Surrounding Thickness nc* — 2.1 nc* nc* nc* (μm)Fiber Thickness (D) (μm) Component A 0.1 — 2.4 2.1 2.7 2.7 Component B3.5 — 0.4 1.5 1.3 1.3 Flatness (L/D) Component A 160 — 6.3 6.2 4.4 4.4Component B 4.5 — 38 8.7 9.2 9.2 Fineness (dtex) Component A 0.03 — 0.500.37 0.37 0.37 Component B 0.63 — 0.07 0.22 0.22 0.22 ProcessingSoundness Carding im* — no* im* im* im* Needle Punching im* — no* im*im* im* Water Jet Entanglement — — no* — — — no*: no fiber splittingyes: fiber splitting occurred nc*: failed to form a surrounding im*:processing was impossible No 11-layered laminate structure was attainedin Comparative Example 2.

EXAMPLES 7-8 and COMPARATIVE EXAMPLE 7

After mixing the composite staple fibers obtained in Example 2 with 1.1dtex, 51 mm polyethylene terephthalate fibers having a circularcross-section at a weight ratio of 50/50 (Example 7), 20/80 (Example 8)or 15/85 (Comparative Example 7), each mixture was subjected to thecarding treatment and the water jet entanglement to obtain a web havinga basis weight of 50 g/m². The wiping capacity of the web was thenevaluated. Although the wiping capacity was satisfactory in Examples 7and 8, inadequate in Comparative Example 7.

COMPARATIVE EXAMPLE 8

After carding 2.2 dtex, 51 mm raw polyethylene terephthalate fibershaving a circular cross-section, the water jet entanglement wasperformed to obtain a web having a basis weight of 50 g/m². The wipingcapability of the resultant web was inadequate.

COMPARATIVE EXAMPLE 9

After carding 1.1 dtex, 51 mm raw polyethylene terephthalate fibershaving a circular cross-section, the water jet entanglement wasperformed to obtain a web having a basis weight of 50 g/m². The wipingcapacity of the resultant web was inadequate.

<Evaluation>

The water-jet entangled webs obtained in Examples 1, 2, 7 and 8 andComparative Examples 7-9 were evaluated on the wiping capacity as awiper and the performance as a base fabric for artificial leather. Theresults are shown in Table 2.

TABLE 2 Comparative Examples Examples 1 2 7 8 7 8 9 Composite staplefiber (wt %) 100 100 50 20 15 0 0 PET fiber (wt %) 0 0 50 80 85 100 100Number of cycles required for 2 2 3 3 5 8 6 disappearance Wipingcapability A A B B C D D Hand feeling A A B B C D D Color development AA A A A A A

Industrial Applicability

The present invention provides a composite staple fiber having itsperiphery covered with a polymer component A, which is resistant to thefiber splitting in the carding and needle punching processes in thenon-woven fabric production, but subject to the fiber splitting only bya subsequent physical treatment such as a water jet entanglement. Theflat ultrafine fibers obtained by splitting the composite staple fiberexhibit satisfactory wiping performance as a result of the sharp edgestructure, and provide a base cloth for artificial leather havingexcellent hand feeling and color development as a result of the specificflat structure.

What is claimed is:
 1. A composite staple fiber having a layeredcomposite structure in which a polymer component A and a polymercomponent B are alternately arranged in a fiber cross-section, whereinthe polymer component B is completely covered with the polymer componentA; the polymer component B and a portion of the polymer component Aexcept for the skin-forming portion has a substantially flat shape, andin the fiber cross-section, the ends of the polymer component B in thelengthwise direction are located 0.05 to 1.5 μm inside the fibersurface; and a weight ratio of the polymer component A to the polymercomponent B is from 90/10 to 10/90.
 2. The composite staple fiberaccording to claim 1, wherein a thickness D in the widthwise directionof each of the polymer component A and the polymer component B in thefiber cross-section is 3 μm or less, and a ratio (L/D) of a length L inthe lengthwise direction to the thickness D is 2 or more for each of thepolymer components A and B.
 3. The composite staple fiber according toclaim 1 or claim 2, wherein the polymer component A is polyester, andthe polymer component B is polyamide.
 4. A process for producing acomposite staple fiber having a layered composite structure in which apolymer component A and a polymer component B are alternately arrangedin a fiber cross-section, wherein the polymer component A and thepolymer component B are melt-spun so that a solubility parameter, SPvalue, and a melt viscosity during the melt-spinning of each componentsatisfy the following Equation 1: η_(A)−η_(B)≦−200×(SP_(A)−SP_(B))  1wherein η_(A) is a melt viscosity (poise) of the polymer component Aduring the melt-spinning, η_(B) is a melt viscosity (poise) of thepolymer component B during the melt-spinning, SP_(A) is a solubilityparameter of the polymer component A, and SP_(B) is a solubilityparameter of the polymer component B.
 5. A non-woven fiber structurecontaining 20 wt % or more of the composite staple fiber according toany one of claims 1 to 3, wherein the polymer component A and thepolymer component B of the composite staple fiber is split at least aportion of the interface between them to form a ultrafine fiber of thepolymer component A having a sharp-edged structure, and fibers thatconstitute the non-woven fabric are entangled.
 6. The fiber structureaccording to claim 5, wherein the non-woven fiber structure is a drynon-woven fabric or a wet non-woven fabric.
 7. The fiber structureaccording to claim 5 or 6, which is entangled with a woven fabric or aknitted fabric into a single structure.
 8. The fiber structure accordingto any one of claims 4 to 7, for use as a wiper.
 9. The fiber structureaccording to any one of claims 4 to 7, for use a base fabric forartificial leather.